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The recent solar minimum has been characterized by an anomalous strong decrease of thermospheric density since 2005. Here we analyze anomalies of mesosphere/lower thermosphere parameters possibly connected with this effect. In particular, nighttime mean LF reflection heights measured at Collm, Germany, show a very strong decrease after 2005, indicating a density decrease. This decrease is also visible in mean meteor heights measured with VHF meteor radar at Collm. This density decrease is accompanied by an increase of gravity wave (GW) amplitudes in the upper mesosphere and a decrease in the lower thermosphere. On the decadal scale, GWs are negatively correlated with the background zonal wind, but this correlation is modulated in the course of the solar cycle, indicating the combined effect of GW filtering and density decrease. [ABSTRACT FROM AUTHOR]

Abstract: A meteor radar to measure hourly mean horizontal winds in the 80–100 km height range and daily temperatures near 90km is operating at Collm (51.3°N, 13°E) since summer 2004. Here we present changes of the meridional wind jet in comparison with temperature fluctuations from August 2004 to May 2006 at time scales of 11–30 days. Whereas in summer no direct correlation between wind and temperature is visible, the meridional circulation at 85km in winter is positively correlated and nearly in phase with temperatures, so that northward/southward winds are generally accompanied by higher/lower temperatures. This behaviour is in accordance with the dynamical forcing of mesopause region temperatures, which is modulated by planetary waves, gravity wave fluctuations and stratospheric warmings. Numerical modelling of MLT planetary waves show that temperature oscillations at 90km and winds at 85km due to those waves have a phase difference of several days, so that planetary waves probably are not the reason for the temperature/wind coupling. [Copyright &y& Elsevier]

Abstract: Radar measurements of mesosphere/lower thermosphere winds are carried out since several decades, now allowing the detection of long-term trends and to distinguish from long-period oscillations connected with the solar cycle or atmospheric decadal variability. Here we analyse Collm (52°N, 13°E) LF mean winds near 95km. The analysis of prevailing winds, tidal amplitudes and phases show (1) a decrease of the summer meridional wind. This change is probably due to modifications of gravity wave filtering through the mesospheric summer jet, (2) a tendency for a decrease of semidiurnal tidal amplitudes, connected with a tidal phase shift. This decrease possibly originates from a combination of CO2 increase and ozone decrease, and (3) an increase of the westerly wind in the mesopause region, probably connected with tropospheric circulation variability and anthropogenic climate change. [Copyright &y& Elsevier]

Focuses on a study which investigated the correlation between mesopause region winds and the north Atlantic oscillation. Connection between upper atmospheric dynamics and tropospheric parameters; Discussion on the mesopause region wind field and European winter tropospheric parameters; Conclusions.

Abstract: The coupling of the neutral atmosphere and the ionosphere through planetary waves (PW) (zonal wavenumber 0–5) is investigated by spherical harmonic analyses of the ionospheric total electron content (TEC). These analyses detect mean variations, standing and travelling waves which are assumed to be signatures of PW. Database used for TEC analyses are 3 years of hourly TEC maps covering the higher middle and polar latitudes. They are regularly produced by DLR Neustrelitz. The obtained results are compared with PW analyses using NCEP/NCAR and Met Office stratospheric reanalyses. Case studies show that signatures of PW occur simultaneously in the middle atmosphere and ionosphere. [Copyright &y& Elsevier]

At the 10th Thermospheric Ionospheric GEospheric Research (TIGER/COSPAR) symposium held in Moscow in 2014 the achievements from the start of TIGER in 1998 were summarized. During that period, great progress was made in measuring, understanding, and modeling the highly variable UV-Soft X-ray (XUV) solar spectral irradiance (SSI), and its effects on the upper atmosphere. However, after more than 50 years of work the radiometric accuracy of SSI observation is still an issue and requires further improvement. Based on the extreme ultraviolet (EUV) data from the SOLAR/SolACES, and SDO/EVE instruments, we present a combined data set for the spectral range from 16.5 to 105.5 nm covering a period of 3.5 years from 2011 through mid of 2014. This data set is used in ionospheric modeling of the global Total Electron Content (TEC), and in validating EUV SSI modeling. For further investigations the period of 3.5 years is being extended to about 12 years by including data from SOHO/SEM and TIMED/SEE instruments. Similarly, UV data are used in modeling activities. After summarizing the results, concepts are proposed for future real-time SSI measurements with in-flight calibration as experienced with the ISS SOLAR payload, for the development of a space weather camera for observing and investigating space weather phenomena in real-time, and for providing data sets for SSI and climate modeling. Other planned topics are the investigation of the relationship between solar EUV/UV and visible/near-infrared emissions, the impact of X-rays on the upper atmosphere, the development of solar EUV/UV indices for different applications, and establishing a shared TIGER data system for EUV/UV SSI data distribution and real-time streaming, also taking into account the achievements of the FP7 SOLID (First European SOLar Irradiance Data Exploitation) project. For further progress it is imperative that coordinating activities in this special field of solar–terrestrial relations and solar physics is emphasized. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of the paper is to answer the question if planetary waves (PW) are capable of propagating into the thermosphere. First the simplest vertical structure equation of the classic tidal theory accounting for a realistic vertical temperature profile is considered. Analysis and simulation show that the well-known normal atmospheric modes (NM), which are trapped in the lower and middle atmosphere, exhibit a wave-like vertical structure with a large vertical wavelength in the thermosphere. Moreover, the reflection of these modes from the vertical temperature gradient in the lower thermosphere causes appearance of the wave-energy upward flux in the middle atmosphere, and in a linearized formulation this flux is constant above the source region. To investigate a possibility of the NM forcing by stratospheric vacillations and to consider the propagation of different PW up to the heights of the upper thermosphere, a set of runs with a mechanistic Middle and Upper Atmosphere Model has been performed. The results of the simulation show that quasi-stationary and longer-period PW are not able to penetrate into the thermosphere. The shorter-period NM and ultra-fast Kelvin wave propagate up to the heights of the lower thermosphere. However, above about 150km they are strongly suppressed by dissipative processes. The role of the secondary waves (nonmigrating tides) arising from nonlinear interaction between the primary migrating tides and quasi-stationary PW is discussed. We conclude that PW are not capable of propagating directly up to the heights of the ionospheric F2 region. It is suggested that other physical processes (for instance, the electrostatic field perturbations) have to be taken into account to explain the observed PW-like structures in ionospheric parameters. [Copyright &y& Elsevier]

Abstract: Maps of electron content retrieved from a 3-dimensional assimilation process of GPS TEC measurements are applied to observe the north polar ionosphere in the evening of 30 October 2003. Their reliability for large-scale imaging is discussed in comparison with GPS data coverage and radar observations. The electron content results are interpreted together with the behaviour of the Interplanetary Magnetic Field (IMF). The images show a region of ionisation expanding across the polar cap from the day to the night side between 20:00 and 21:30UT. A patch-like structure is observed at successive times with locations approaching the night side ionosphere. At corresponding time the IMF B z was steadily negative. To explain the observations, an anti-sunward plasma transport is proposed. Consecutively to 21:30UT a low electron content is imaged polward of 70°N coinciding with an increasing and then positive IMF B z . During a further phase of negative IMF B z an enhanced electron content appears at night side mid-latitudes beyond 50°N. The assimilation images are a useful observational tool of the large-scale distribution of electron content, especially together with further data of ionospheric parameters. [Copyright &y& Elsevier]

Mesosphere/lower thermosphere wind data sets from three midlatitude sites and UKMO assimilated wind data in the height range 0–55 km at 55°N were used to show the altitudinal and longitudinal variability of mean winds and planetary waves at mid-latitudes during solstices. In spite of the existence of longitudinal differences of the prevailing winds and the annual and semiannual oscillations, certain common features of the zonal wind height profiles are visible in the height range 10–100 km. The maxima of the mean annual winds and of the intensities of the annual and semiannual oscillations occur near the stratopause. In the height range 80–100 km there is an increase in the annual mean winds and in the amplitudes of the annual and semiannual oscillations; also the semiannual oscillation is larger than the annual one. Minima of the annual/semiannual oscillation amplitudes at heights of 85–95/80–85 km are accompanied by corresponding phase changes of 180 degrees in relation to those values near the stratopause. The height structure of meridional wind parameters is more complicated, with dependences on longitude and height. Longitudinal variability in the intensity of planetary waves was also found. [Copyright &y& Elsevier]